The reaction of maleic diesters with certain diamines is known, as illustrated by the work of Yu. T. Tanckuk and I. A. Ral'chuk, J. Organic Chem. U.S.S.R., Vol. 14, pp. 2083-2088 (1978). In this work, the reported reaction products are a polyamide that retains the maleic acid double bond, an addition product in which each amine group of the diamine has added by Michael reaction to the double bond of a maleic diester, and a maleic diester derivative in which one of the ester groups has been replaced by an amide group (an amic ester).
Low temperature cure coating compositions based on amine-reactive polymers, as illustrated by U.S. patent application Ser. No. 346,329, filed Feb. 5, 1982, and now abandoned, and U.S. patent application Ser. No. 377,504, filed May 12, 1982, now U.S. Pat. No. 4,446,280, are known to me. These coating compositions are based upon solvent borne, solution polymers containing activated ester groups. In Ser. No. 377,504, the polymer thereof is crosslinked by the use of an amine-terminated triazine resin, to give a film with good resistance properties. However, the coatings are often rather brittle. In Ser. No. 346,329, the crosslinking agent may be a long chain diamine such as 4,7-dioxo-1,10-decanediamine (DODA) or a shorter aliphatic diamine such as 1,6-hexanediamine. Flexibility can be obtained by using a long chain diamine such as DODA, but at the expense of hardness. In fact, it is difficult to prepare films with a Knoop hardness over 3 when using DODA. Moreover, when a shorter aliphatic diamine is used, it is difficult to obtain an acceptable crosslink density. The six carbon chain of 1,6-hexanediamine is too short to provide efficient utilization of the activated ester groups. Therefore, there has existed an urgent need for a crosslinking agent that makes possible low temperature cure, that yields a hard yet flexible film having good resistance properties, and that provides efficient utilization of the amine-reactive groups of the crosslinkable polymer. Hence, the provision of such a crosslinking agent and of compositions based thereon useful, for example, for coatings and adhesive applications, would constitute a significant advance in the art.